Pathologic patterns and survival in chronic hypersensitivity pneumonitis.

The objective of the study was to examine the relationship of pathologic pattern and prognosis in hypersensitivity pneumonitis (HP). We analyzed 24 cases of subacute (cellular, nonfibrotic) and 25 cases of chronic (fibrotic) HP. Nineteen (79%) of the subacute cases showed a pattern of bronchiolocentric interstitial pneumonia and 5 (21%) a pattern mimicking cellular nonspecific interstitial pneumonia (NSIP). Giant cells or granulomas or Schaumann bodies were present in 19 cases (79%). Eighteen (72%) chronic cases showed a pattern resembling usual interstitial pneumonia (UIP), but, in most cases, with more peribronchiolar fibrosis than one would expect in UIP. Three fibrotic cases (12%) had only peribronchiolar fibrosis, whereas 4 (16%) resembled fibrotic NSIP. Giant cells or granulomas or Schaumann bodies were present in 22 (88%) cases. Areas of subacute HP were present in 12 cases with a UIP-like pattern. Only 2 UIP-like cases could not be morphologically distinguished from idiopathic UIP. The median survival for patients who had no fibrosis was 22.4 years; for patients with a fibrotic NSIP pattern was 2.1 years; and for those with a UIP-like pattern 2.8 years (not statistically different). Patients with a pattern of only peribronchiolar fibrosis had a median survival of 11.3 years. These data confirm that the presence of fibrosis is associated with a generally poor prognosis in patients with HP, and suggest that pure peribronchiolar fibrosis may portend a longer survival than does a UIP-like or fibrotic NSIP-like pattern of fibrosis. Most cases of chronic HP have distinctive pathologic features, but a small percentage of cases cannot be pathologically distinguished from UIP.